1. Field of Invention
The present invention relates to an amplifying circuit in a receiver. More particularly, the present invention relates to a preamplifier and method for calibrating offset voltages therein in a receiver.
2. Description of Related Art
For a conventional preamplifier in a receiver, there are usually a number of stages of cascade-connected amplifying circuits in the preamplifier. Small differential signals are input into the preamplifier and sequentially amplified by the cascade-connected amplifying circuits to be the large differential signals. However, each of the amplifying circuits in the preamplifier often has more or less offsets in itself, such that the amplified differential signals output by the amplifying circuit may have different common voltage levels therebetween.
As a result, the large differential signals output from the preamplifier may have the problem of duty cycle distortion, and the skew tolerance of the receiver could be thus decreased.